1. Field of the Invention
This invention relates to a speaker for use in various types of acoustic apparatuses, and more particularly, to a speaker whose speaker frame is molded of a heat resistant plastic resin and does not need any adhesive to assemble its magnetic circuit.
2. Prior Art
It has been known, for example from, Japanese Patent Laid-Open Publication Sho 58-171197, Japanese Utility Model Post-Examination Publication Sho-63-49993 and Japanese Patent Laid-Open Publication Sho 60-180300 and others, that a speaker frame may be made of polycarbonate or other engineering plastic excellent in resistance to heat, mechanical strength, resistance to abrasion, and the like.
Among them, Japanese Utility Model Laid-Open Publication Hei 2-21998 discloses an arrangement for easily assembling a magnetic circuit to a speaker frame by sequentially stacking, from the base, a lower plate, a plastic magnet, an upper plate and a frame such that coupling projections standing from the plastic magnet engage with holes provided in the other members, then heating the assembly to secure the coupling projections of the plastic magnet to the other members due to thermal fusion, and fixing the upper plate to the bottom of the plastic frame by deforming the coupling projections of the upper plate to sit on the bottom plate of the plastic frame. This technique is certainly excellent in that it can make up a speaker having a plastic frame without using an adhesive for coupling respective constituent elements.
The above technique, however, requires coupling projections standing from some locations of upper and lower surfaces of the ring-shaped plastic magnet and engaging holes provided in the upper and lower plates to receive the coupling projections. Therefore, many steps are required to prepare respective components of the magnetic circuit, and any error in positional relations between coupling projections and holes makes the assemblage of the magnetic circuit difficult.
Moreover, although the known technique does not need caulking, fixing by bolts or bonding with an adhesive, it still needs hot bonding by using a high-frequency heater, and hence requires a large-scaled apparatus in the manufacturing process. Therefore, and for other reasons, the known technique fails to reduce the cost of the speaker, which and other factors still remain as problems to be solved.